Amplifying apparatuses that amplify signals in a wireless communication device, etc., employ envelope tracking aimed at improving amplification efficiency by applying a voltage similar to the envelope of a transmission signal as the voltage of a power amplifier. A method of improving the amplification efficiency involves switching a power source according to the amplitude of the envelope of the transmission signal (see, e.g., Japanese Laid-Open Patent Publication Nos. 2008-301135, 2005-252817, and 2000-077953). Higher power efficiency while achieving transmission signal quality equivalent to that in the case of generating a fixed voltage in the power amplifier is demanded of wireless communication devices.
In the conventional technologies described above, however, since the power source is switched with a load current flowing through the amplifier, distortion is caused to a waveform of the voltage supplied to the amplifier. Distortion of the waveform causes a problem in that the amplifier is unable to accurately amplify the signal, resulting in deteriorated signal quality. In particular, in a high power amplifier (HPA), due to the flow of a load current of several amperes, the distortion caused to the waveform of the voltage supplied to the HPA results in greatly deteriorated signal quality.